1. Field of the Invention
The invention relates to a filament lamp. The invention relates especially to a filament lamp for irradiation of an article to be treated with light which is emitted for purposes of heating of the article to be treated.
2. Description of Related Art
In semiconductor manufacturing, generally, heat treatment is used in different processes, such as a layer formation, oxidation-diffusion, diffusion of impurities, nitriding, layer stabilization, silicide formation, crystallization, ion implantation activation and the like.
To increase the yield and quality in semiconductor manufacture, rapid thermal processing RTP is desirable, in which the temperature of the article to be treated, such as a semiconductor wafer or the like, is rapidly raised or lowered. In RTP a heat treatment device of the light irradiation type (hereinafter also called only a heating device) using light irradiation from a light source, such as a filament lamp or the like, is widely used.
A filament lamp in which there is a filament within a bulb of transparent material is a typical lamp in which light can be used to produce heat since, in this connection, at least 90% of the input power is converted to heat and since heating is possible without contact with the article to be treated.
In the case of using this filament lamp as a heat source to heat a glass substrate and a semiconductor wafer, the temperature of the article to be treated can be raised/lowered more quickly than in a resistance heating process. This means that, by heat treatment of the light irradiation type, for example, the temperature of the article to be treated can be raised to at least 1000° C. in from ten to a few dozen seconds. After light irradiation has been stopped, the article to be treated is rapidly cooled. This heat treatment of the light irradiation type is normally done several times.
In this connection, if the article to be treated is, for example, a semiconductor wafer (silicon wafer), when a nonuniformity occurs as the semiconductor wafer is heated to at least 1050° C., a phenomenon called slip occurs in the semiconductor wafer, i.e., a defect of crystal transition, by which the danger arises that scrap will be formed. If RTP of a semiconductor wafer is carried out using a heat treatment device of the light irradiation type, heating must be performed, a high temperature maintained and then cooling must produced such that the temperature distribution of the overall surface of the semiconductor wafer becomes uniform. This means that, in RTP, there is a need for very precise temperature uniformity of the article to be treated.
In the case, for example, of a uniform physical property of the overall surface of the semiconductor wafer in heat treatment of the light irradiation type, the temperature of the semiconductor wafer does not become uniform even if light irradiation is performed such that the irradiance becomes uniform on the entire surface of the semiconductor wafer. In this connection, the temperature of the peripheral region of the semiconductor wafer is low. This is because in the peripheral region of the semiconductor wafer heat is radiated from the semiconductor wafer side. As a result of this heat release, a temperature distribution forms in the semiconductor wafer.
As was described above, in a semiconductor wafer slip occurs when a nonuniformity in the temperature distribution of the semiconductor wafer arises in the heating of the semiconductor wafer to at least 1050° C.
In order to make the temperature distribution of the semiconductor wafer uniform, it is therefore desirable to carry out light irradiation such that the irradiance on the surface of the peripheral area of the wafer is greater than the irradiance on the surface of the middle wafer area in order to equalize the temperature drop as a result of heat radiation from the side of the semiconductor wafer or the like.
Patent document 1 (JP HEI 7-37833 A) discloses a conventional heating device in which light emitted by a filament lamp is used to heat a glass substrate and a semiconductor wafer. This heating device has the arrangement shown in FIG. 6 in which in a chamber of transparent material there is the article to be treated and on a top step and a bottom step, therefore on two steps outside of this chamber there are several opposed filament lamps at top and bottom, and moreover, crossing one another, and in which the article to be treated is irradiated with light from both sides and heated.
FIG. 7 is a perspective in which the above described device is shown simplified and the filament lamps located on the top step and bottom step, therefore on the two steps, for heating and the article to be treated are shown. As shown in FIG. 7, the filament lamps for heating which are located on the top step and the bottom step, therefore on the two steps, are arranged such that the bulb axes cross. The article to be treated can therefore be heated uniformly. Furthermore, this device can prevent a temperature drop by the action of heat radiation in the peripheral area of the article to be treated. For example, with respect to the article to be treated, the lamp output of the filament lamps for heating L1, L2 located on the two sides of the top step is made larger than the lamp output of a lamp L3 for heating located in the middle area. The lamp output of the filament lamps for heating L4, L5 located on the two sides of the bottom step is made larger than the lamp output of a lamp L6 for heating located in the middle area. In this way, the amount of temperature drop by the action of heat radiation in the peripheral area of the article to be treated can be equalized, the temperature difference between the middle area and the peripheral area of the article to be treated can be reduced and the temperature distribution of the article to be treated can be made uniform.
In the above described conventional heating device it has however been found that the following disadvantages arise.
Specifically, for example, in the case in which the article to be treated is a semiconductor wafer, generally, a film of a metal oxide or the like is formed on the surface of the semiconductor by a sputtering process or the like, or foreign ion material is doped by ion implantation. The layer thickness of this metal oxide or the density of the foreign ions on the wafer surface has a local distribution which is not always centrosymmetric to the middle of the semiconductor wafer. For example, on the example of the density of foreign ions, there is a case according to FIG. 7 in which the density of foreign ions changes in a narrow, special region which is not centrosymmetric to the middle of the semiconductor wafer. Even if irradiation with light is performed such that, in this defined region and in the other region, the same irradiance is obtained, there is a case in which, between the rate of temperature rise in the above described defined region and the other region a difference forms. The temperature of the defined region described above does not always agree with the temperature of the other region.
The above described conventional heating device makes it possible to relatively easily equalize the effect of the temperature drop by heat radiation in the peripheral area of the region to be treated, to prevent a temperature drop in the peripheral area and to make the temperature distribution of the article to be treated uniform in a certain narrow region with a total length which is less than the emission length of the lamp, however, as is shown, for example, in FIG. 7, a region outside of the above described certain region is also irradiated with light, even if light irradiation is performed with an intensity which corresponds to the property of this certain region. Therefore, control cannot be exercised in such a manner that the above described certain region and the other region are shifted into suitable temperature state. This means that the irradiance in the above described, narrow defined region cannot be controlled such that the two temperatures become uniform. At the treatment temperature of the article to be treated, therefore, an unwanted temperature distribution occurs, resulting in the disadvantage that it becomes difficult after light heat treatment to impart the desired physical property to the article to be treated.
As is shown in FIG. 8, for example, in patent document 2 (JP 2002-203804 A and corresponding U.S. Patent Application Publication 2004/0112885 A1), a heat treatment device is disclosed in which there are a first lamp unit and a second lamp unit in the lamp housing. In the first lamp unit, several U-shaped double-end lamps in which there are feed devices for the filaments on the two ends of the bulb are arranged perpendicular and parallel to the page of the drawing. In the second lamp unit, several straight, double-end lamps which are located under the first lamp unit and in which on the two ends of the bulb there are feed devices for the filaments are located along the page of the drawings in the direction perpendicular to the page of the drawing. In this heat treatment device, an article, such as a semiconductor wafer or the like, which is located underneath the second lamp unit, is heat treated.
In this connection, it is shown that this heat treatment device yields a device which exercises control such that the U-shaped lamps of the first lamp unit which are located above the connecting part have a high output in order to increase the temperature of the connecting part on a support ring on which the article to be treated is placed, this connecting part having a tendency to have a lower temperature than the remaining region.
It is shown in patent document 2 that this heat treatment device is used essentially as follows.
First, the heating area of the semiconductor wafer as the article to be treated is divided into several zones which are centrosymmetric and concentric. By combining the distribution of the illuminance by the respective lamp of the first and second lamp units with one another, artificial illuminance distribution patterns are formed which correspond to the respective zone and which are centrosymmetric to the middle of the semiconductor. Thus, heating is carried out according to the temperature change of the respective zone. In this connection, the semiconductor wafer which constitutes the article to be treated is rotated to suppress the effect of the scattering of the illuminance of the lamp radiation. This means that the respective concentrically arranged zone can be heat treated at an individual illuminance.
Temperature control is possible by the technique described in patent document 2, therefore, in the case in which the narrow, defined region for the article to be treated is centrosymmetric to the middle of the semiconductor wafer. However, if the defined region is not centrosymmetric to the middle of the semiconductor wafer, the above described disadvantage cannot be advantageously eliminated because the semiconductor wafer which is the article to be treated is rotated.
Furthermore, in such a heat treatment device, it is possible for the following disadvantages to occur in practice. Specifically, a U-shaped lamp is formed of a horizontal region and a pair of vertical regions. However, since only the horizontal region in which the filament is located contributes to emission, the individual lamps are apart from one another over a space which cannot be ignored. Therefore, it can be imagined that a temperature distribution forms in the region which is located directly underneath this space.
Even if the distributions of the illuminance by the respective lamp of the first and second lamp units which corresponds to the respective zone are combined with one another and an artificial illuminance distribution is formed which is centrosymmetric to the semiconductor wafer, specifically the illuminance in the region directly underneath the above described space changes (decreases) relatively quickly. Therefore, it can be imagined that it is relatively difficult to reduce the temperature distribution which arises in the vicinity of the region which is located directly underneath the above described space, even if an attempt is made to carry out heating according to the temperature change of the respective zone.
Furthermore, such a heat treatment device is undesirable with respect to making the space smaller, since recently there has been a trend toward an extreme reduction in the size of the space (mainly vertically) for arrangement of the lamp units, and since therefore when a U-shaped lamp is used, a space corresponding to the vertical regions of the lamp is required.
FIG. 9 is a schematic perspective view of the basic arrangement of a filament lamp as disclosed in commonly-owned, co-pending U.S. patent application Ser. No. 11/362,788 (Patent Application Publication 2006/0197454 A1) relative to which one of the inventors of the present invention is a co-inventor and constitutes a precursor to the present invention. This filament lamp has several filaments in a bulb and separate control of emission and the like of the each filament is possible. By using a heat treatment device of the light irradiation type with light source parts in which these filament lamps are arranged parallel to one another, compared to the case of using a conventional filament lamp with a single filament in the bulb several filaments can be supplied individually. This makes it possible, even in the case of a shape of the defined region on the substrate-like article to be treated asymmetrical to the substrate shape, to irradiate this defined region with light of a certain light intensity. Therefore, it becomes possible, even in the case of an asymmetrical distribution of the degree of the local temperature distribution on the substrate-like article to be heat treated to the substrate shape, to uniformly heat the article to be treated. As a result, a uniform temperature distribution can be implemented over the entire article to be treated. When the heat treatment device of the light irradiation type using this type of bulb is compared, for example to the heat treatment device of the light irradiation type described in patent document 2, in which U-shaped lamps are used, in the heat treatment device of the light irradiation type of this co-pending application, it is possible to make the filaments lamps used in the form of a rod-shaped tube. The space corresponding to the vertical regions of the U-shaped lamp is therefore no longer necessary, and a reduction in size can be achieved.
The basic arrangement of the filament lamp shown in FIG. 9 is further described below. On the two ends of the bulb of this filament lamp, hermetically sealed portions are formed in which metal foils are inserted. In the bulb, there are several filament bodies (in FIG. 9, two bodies) which are formed of filaments and leads for feeding the filaments. In this connection, each filament body is arranged such that, in an arrangement of several filament bodies in the bulb, the filaments are arranged in rows in the lengthwise direction of the bulb.
There is an insulator, for example, of silica glass between the filaments which are arranged in rows in the lengthwise direction of the bulb. In FIG. 9, a lead which borders one end of a filament in one of the filament bodies passes through a through opening in the insulator. The outside of the point which is opposite the filament of the other filament body is covered with an insulating tube and is electrically connected to a metal foil which has been inserted in the hermetically sealed portion on one side of the end of the bulb. The lead which borders the other end of the filament in one of the filament bodies is electrically connected to a metal foil which is inserted in the hermetically sealed portion on the side of the other end of the bulb.
Likewise, one lead which borders one end of a filament in the other filament body passes through the through opening in the insulator. The outside of the point which is opposite the filament of the one filament body is covered with an insulating tube and is electrically connected to a metal foil which is inserted in the hermetically sealed portion on one side of the end of the bulb. The lead which borders the other end of the filament in the other filament body is electrically connected to a metal foil which has been inserted in the hermetically sealed portion on the side of the one end of the bulb.
An outer lead is connected to the end of the metal foil which is inserted in the hermetically sealed portion which is opposite the end to which the filament body is connected, such that the outer lead projects to the outside from the hermetically sealed portion. Two outer leads are therefore connected via the metal foil to the respective filament body. A feed device is connected to each filament via the outer leads. In this way, in the filament lamp, each filament of the respective filament body can be supplied individually.
The filament lamp shown in FIG. 9 had the following disadvantages.
The two ends of the filament lamp are hermetically terminated by a pinch seal. The pinch seal takes place, for example, by the outer leads being attached to the metal foils after welding of the outer leads and the leads of the filament body, the end of the bulb on which the metal foils are located being burned with a torch, and the metal foils being clamped from both sides by the metal shape which was produced in the form of the desired sealing area.
In the filament lamp which is shown in FIG. 9, in the hermetically sealed portion on the end of the tube, twice as many metal foils as the number of filaments are inserted in order to supply several filaments independently of one another. If an attempt is made to increase the number of filaments, therefore the number of metal foils inevitably increases. When a plurality of metal foils (for example, at least four) is required for the filament lamp shown in FIG. 9, it is necessary for the respective metal foil to have a certain cross sectional area to prevent fusing in the supply of the filaments. Moreover, it is necessary for the individual metal foils to be electrically insulated from the other metal foils. If an attempt is made to pinch a plurality of metal foils in a right-angled hermetically sealed portion, the region in which the metal foils are sealed is also made larger. For this reason, there were cases in which difficulties occurred in manufacture or poor sealing such as leaks and the like occurred more often. When poor sealing, such as a leak or the like occurs, air is mixed into the bulb of the filament lamp, resulting in the disadvantage of burning through by oxidation of the filaments. Likewise, the silica glass in the hermetically sealed portion is expanded by the metal foils being oxidized by the added air and expanding. Finally, the disadvantage of damage to the bulb occurs, by which the filament lamp becomes unusable. It can be imagined that a plurality of metal foils are necessary when it is necessary to control the local distribution with high precision in semiconductor heating.
The inventors conducted numerous studies to devise a filament lamp which has high reliability by its having a sealing arrangement in which these disadvantages, such as poor sealing and the like, do not occur, and thus they have completed the invention, as is described below.